This invention concerns a method to prepare an aluminosilicate polymer, and the use of the polymer obtained by said method in the treatment of photographic processing effluents.
Aluminosilicate polymers are known. A filamentous tubular crystallized aluminosilicate designated imogolite occurs naturally in volcanic ash. U.S. Pat. Nos. 4,152,404 and 4,252,779 describe the synthetic preparation of substances related to imogolites. U.S. Pat. No. 5,888,711 describes a method to obtain directly a fibrous aluminosilicate polymer of high purity of formula AlxSiyOz, where x:y is 1 to 3 and z is from 1 to 10. A variant of this method that affords a morphological variety of this aluminosilicate polymer is described in French Patent application 2 767 128.
The object of this invention is an improvement of the synthesis of aluminosilicate polymers as described in U.S. Pat. No. 5,888,711 or French Patent 2 767 128, whereby these polymers are obtained faster, more simply, and at lower cost.
The method of the invention, to prepare an imogolite-type aluminosilicate polymer, comprises the following steps:
(a) A mixed aluminium-silicon alkoxide, or a precursor of a mixed aluminium-silicon compound is treated with an aqueous alkali at a pH of between 4.5 to 6.5, keeping the molar concentration of aluminium between 5xc3x9710xe2x88x924 and 10xe2x88x922 and the Al/Si molar ratio between 1 and 3.
(b) The mixture obtained in step (a) is heated at a temperature lower than 100xc2x0 C. for sufficient time for the reaction to go to completion.
(c) The residual ions are removed from the mixture obtained in step (b).
This method is characterized in that step (a) is carried out in the presence of silanol groups, and in that after step (a) and before step (b) ripening step at ambient temperature is included.